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2 Earthquakes The shaking caused by the sudden movement of the crustScientists estimate that over one million earthquakes happen every year.Approximately one earthquake every thirty seconds.Most so small that no one notices them are recorded by seismographs.

3 Several thousand per year actually move the surface of the Earth.About 20 per year cause severe changes in the Earth’s surface.These have the potential to cause serious damage to buildings and dramatic loss of life in populated areas.

4 Seismic Waves Waves travel from the break outward.Main cause is faulting.If they occur on the ocean floor they can cause giant waves called tsunamisTravel at km/hr10 to 20 meters high when they hit the coast.

15 Volcanoes Magma- melted rock below the surfaceLava- when it reaches the surfaceVolcano - where lava reaches the surfaceLava lets us see what is below the crustDifferent types of lavaDark colored, runny lava flows quietlyLight colored hardens inside, pressure builds and it explodes.Gas bubbles can form pumice and scoria

16 Rock fragments Thrown out in eruptions Different sizesVolcanic dust- like flourVolcanic Ash- grains of riceCinders- about the size of a golf ballVolcanic bombs- a few centimeters to several meters across

17 Types of Volcanoes Three different typesCinder cone formed by piling up rock fragments from explosive eruptionsNarrow base and steep sidesShield volcanoes runny lava pouring out covers the ground in layerslarge area, gentle slope - Hawaii